In the fuel loading industry where a fuel truck is being loaded with a liquid or fuel that is often flammable, in order to meet mandated safety requirements, several parameters of the fuel transfer process are routinely monitored for compliance with loading operations standards. These parameters include, commonly, assuring that a static ground is present in order to prevent sparking and monitoring tank capacity in order to avoid an overfill condition and possible fuel spill.
In addition, vapor recovery during the filling process, in order to meet environmental and safety guidelines, is becoming increasingly important. Many of the current fuel loading monitoring systems are inadequately equipped for detecting that vapor recovery is being properly implemented.
In order to minimize the release of vapor into the atmosphere, as fuel is loaded into a modern tanker, the vapor in the vehicle is exhausted through a pressure valve at the top of the tank and run through piping that terminates in a coupling typically mounted on the rear of the vehicle. Many loading racks have a vapor recovery system to capture these vapors and either burn them off or otherwise process them.
Operators of fuel loading stations need to make sure that the vapor hose is connected to prevent vapor being exhausted into the atmosphere. Thus, these operators need an automatic system to prevent the loading operation from commencing without the vapor capture and monitoring systems being in place.
Currently, there are two approaches: 1) vapor monitoring in which a thermistor sensor is inserted into a vapor recovery hose. The thermistor sensor consists of two thermistors with one thermistor being a reference and isolated from the vapor flow and a second sensing thermistor positioned in the vapor flow. In operation, when the vapor is flowing, the thermistor in the flow is cooled by the vapor and the control electronics senses a difference in the respective thermistor resistances and indicates a vapor flow is established. This method is effective, however, it is known to take a not insignificant amount of time after the product or liquid is loaded before vapor starts to flow in order to make a reading. To deal with this delay, the operator must set a grace period (usually 1 to 5 minutes) before which the vapor monitoring system cannot be relied on to have sensed a vapor flow. If no vapor flow is detected after the grace period the controller stops the loading of fuel. The issue is that significant vapor can be sent into the atmosphere if the hose is not connected during this grace period while fuel is being added.
A second method of vapor recovery uses a switch mounted on the vehicle that is activated by the coupling of the vapor recovery hose. This switch is connected in such a way that it enables on-board vehicle electronics (if so equipped) to prevent fuel loading without an indication that the vapor hose is connected. There are several weaknesses to this method including: 1) the switch is external to the truck and easily bypassed with locking pliers and the like; 2) not all vehicles have on-board electronics that would be compatible with the switch; and 3) the load rack operator is ultimately responsible for making sure the vapor recovery takes place. The loading rack operator, therefore, needs to confirm for themselves to prove to the appropriate regulatory authorities that they, and not the fuel truck drivers (many of whom are known to bypass the system in order to load up faster), are assuring that the vapor hose is connected.
Traditionally, known vapor recovery systems use only the pressure from the tank to exhaust the vapor from the tank with a poppet valve located on the truck outlet to prevent vapors from leaking unless a vapor hose is connected. The rack side hose generally only has a pin that opens the poppet valve on the tanker connection. Recently, however, many rack operators have started using vacuum assist vapor recovery systems that contain a vacuum to draw residual vapor from the hose after the tanker has disconnected.
In addition to the vacuum assist couplings on the rack side of the hose there are now hoses with integral poppet valves to further reduce vapor from escaping during fuel transfer.
What is needed, however, is a system for automatically disabling fuel transfer if it is determined that the vapor recovery system is not properly connected. Such a system must be one that can be retrofitted onto existing trucks and racks and one that cannot be easily bypassed.